C. DOBBLL 177 



(Jennings, 1911 a) ; and (2) that homogamy occurs in addition (Jennings, 

 1911a). The inference ft-om these two facts seems clearly to be that 

 " inbreeding " is the rule — at least in Paramecium. 



117. An extreme case of interconj ligation has been recorded by 

 Jennings'. He obtained no less than nine successive interconjugations 

 in the descendants of the same individual. " The progenitor of the race 

 vfas a single individual ; its progeny conjugated among themselves ; from 

 these conjugants a single exconjugant was taken and allowed to multiply 

 till there was conjugation among these." An exconjugant was again 

 isolated and allowed to multiply — and so on, nine times in succession 

 (in the complete experiment). It appears — though Jennings does not 

 emjjhasize the fact in this connexion — that the mortality among the 

 final descendants was excessively high. 



118. A case of conjugation between very closely related individuals 

 is recorded for the colonial Vorticellid Opercularia by Euriques (1907). 

 He states that male and female conjugants (§§ 6, 14) are formed by an 

 original " indifferent " individual'- — incapable of conjugating — dividing 

 into a large and a small product, the latter dividing again into two 

 smaller individuals. The large individual becomes a female conjugant, 

 the two small individuals males. It is stated that conjugation may 

 occur between males and females formed in this manner from the same 

 indifferent individual''. Calkins (1912) has even recorded a case of 

 conjugation in Blepharisma in which the two conjugants were the 

 products of fission of the same individual — " the closest case of paedo- 

 gamy in ciliated protozoa on record." Death followed conjugation — as 

 in all eases observed in Blepharisma. 



119. The general conclusion to be drawn from the recorded cases 

 of interconj ugation is by no means clear. It is evident that closely 

 related individuals will conjugate readily with one another : but the 

 ultimate effect of such conjugation on the jjrogeny is not evident, 



1 Jennings (1913, expt. 13). Jennings speaks of this interconjugation as " self- 

 fertilization — which it certainly is not. He obtained eight successive interconjugations — 

 " to avoid, so far as possible, the heterozygotic condition "' — and then studied the effects 

 of conjugation at the ninth. Since the general conclusion from this was that conjugation 

 "increases greatly the variability," I cannot understand how previous conjugations are 

 supposed to eliminate "the heterozygotic condition." The mathematical treatment of 

 "self-fertilization" seems to have no bearing on the actual phenomena concerned. 



'^ It may be noted that Enriques (1907) states that in the Vorticellid Carclieshini, the 

 branches of the colony are differentiated as males, females, and " indiflerents." This was 

 not confirmed by Popoiif (1908 «). 



^ I do not know how it was possible to make this extremely difficult observation with 

 any certainty. 



